There is no way to simply *make* a person understand that they are important. You just need to stick by them, no matter what, and show them every day of their lives that they are apart of something bigger than themselves and that you both need to support one another :)
Respect goes a long way. Society often makes individuals with disabilities out to be "lesser than" and in reality these individuals have so much to give. Through provide respect and looking past the disability you empower the individual.
everyone has strengths and weaknesses (its a cliche for a reason :P ) just because you might have some sort of disability doesn't mean you are useless, in fact usually people with disabilities have had to find different ways to do certain things in order to compensate with their disability (this means that these people are often more self-aware than the average person, which is a really good and beneficial trait)
It's important, however you choose to approach the subject, to avoid being patronizing, or talking to someone as if they are "broken", whatever your intention. Helping someone realize their self-worth is something that you can do simply by accepting them into your life and treating them as you would anyone else (while still looking out for whatever accommodations might be necessary). Beyond that, you can help encourage them to try new things or participate in events they would normally have backed away from, and educate your friends and family about the specific disability so that they may also support the person as well.
Treat them as you would any other friend or co-worker (depending on what area you know them in). I can tell you from experience as someone with a disability that it is very hurtful to be treated as less or seen as needing "extra". People with disabilities may need accommodations but do not overemphasize this. Ask the person if they need support only if they look like they made need it or come to an agreement with them that they will ask if need be. Lastly, educate yourself on the disability. All disabilities are different and with disabilities such as hearing loss or visual impairment what helps one person may not help another due to differiences in the severity. Open communication is key.
The most important thing to know when interacting with people with disabilities is that they are people. And just like all people, they are very different, including being different in how they are with disability issues.
As a person with a physical disability.. I feel like you should start by treating that person like any other human being. I am one person who often gets offended when people never give me the chance to actually do things or at least try.
The most important thing to know is they are human beings and people and they need support, some people ignore the people who have disabilities but that is not right, we have to support them and help them because sometimes people never care about those people who have disabilities so they think that they are not needed or important in the society, so all I can say is try to care and support those people because of their disabilities they feel so lonely, they are human beings, it is one of their rights to care and support them
Just be nice to the person! Listen carefully to them, especially if there is a speech impediment. Encourage them to participate in society's everyday activities, such as work and voting whenever possible. Open doors for them, and be ready to help with other mobility challenges such as tough terrain. Talk to instead of over or about the person. A small amount of basic kindness and etiquette goes a long way in helping people feel important!
Your body doesn't define your capability as a human being. Everyone has an equal opportunity to bring something amazing to this world, and even though there may be physical barriers, in the end, it is what one does that reflect their character, not their body.